Runlevel in Linux Operating System

Runlevel is a state or mode of operating system in Linux. There are "seven" runlevels which is represented by a single digit integer. It is one of the most important term in Linux. Linux kernel supported and differentiate all levels. Runlevels defiened by the services and those services stored in directory i.e /etc/rc.d/.

Seven Runlevels are as follows:

  • Runlevel 0: It means System in hault state, there is no activity.

  • Runlevel 1: It means system is in "single user" mode . Which are rarely used.

  • Runlevel 2: It means system is in Multiple users mode but no network file system ( NFS ) are there. Which also rarely used.

  • Runlevel 3: It means system is in multiple users, Command line mode. It is a default runlevel in most of the linux system.

  • Runlevel 4: It means system is in User-definable mode . That is not in used.

  • Runlevel 5: It means system is in mutiple users mode with GUI ( graphical user interface ). This one is the standard runlevel.

  • Runlevel 6: It is used when the user want to restart the system basically for the Reboot sake.

Important things:

You can check your runlevel by command - runlevel

The default runlevel for a system is specified in the - /etc/inittab file.